1. Field of the Invention
Provided is a method of processing dielectric fluids, particularly hydrocarbon fluids, by discharges created in the fluids through the use of mobile charge carriers. The method can further refine the fluids and/or improve the viscosity and flowability of the fluids.
2. Description of the Prior Art
The dynamics of charged particles in dielectric media has been described by several authors, Melcher, James R. Continuum Electromechanics, Cambridge, Mass.: MIT Press, 1981; and Jones, Thomas B. Electromechanics of Particles, Cambridge University Press 1995. Particle motion in these heterogeneous fluids, where the particles can be either gas, liquid, or solid, can be explained by either electrophoresis, forces on charged particles due to a uniform electric field, dielectrophoresis, or forces on dielectric particles due to a changing field. Although the dynamics of these systems are well known the collisional charge exchange mechanisms between particles have not been fully described. At low electric field, where no discharges occure, some of the processes have only recently been described [W. D. Ristenpart, J. C. Bird, A. Belmonte, F. Dollar & H. A. Stone, “Non-coalescence of oppositely charged drops,” Nature 461, 377-380 (2009)]. The prior art has been devoid of a workable understanding of the plasma discharge processes which occur at high electric fields and of a strategy for controlling, and application of the electrical discharges which form when charge carriers collide.
Heavy crude oils are petroleum fuels which do not flow easily. They are classified with an API gravity (API°=141.5/SG -131.5, where SG is the specific gravity of the oil) of less than 20°. There are many subterranean formations containing heavy, i.e., viscous, oils. Such formations are known to exist in the major tar sand deposits of Alberta, Canada and Venezuela, with lesser deposits elsewhere, for example, in California, Utah and Texas. The API gravity of the oils in these deposits typically ranges from 10° to 6° in the Athabasca sands in Canada to even lower values in the San Miguel sands in Texas, indicating that the oil is highly viscous in nature. Typically, crude produced from these areas contain large amounts of water in addition to inorganic contaminants such as salts. The high density and viscosity of these crudes make them difficult to transport. In addition, their processing in conventional refineries is not possible. Hydrotreatment has been used as a method for upgrading heavy oil typically employing chemicals, catalysts, and ultrasound. Such hydrotreating methods are disclosed in U.S. Patents, for example U.S. Pat. Nos. 3,576,737; 7,651,605; 5,824,214 to name a few.
These higher density oils are at a much higher viscosity in comparison to traditional oils. Heavy and extra heavy oils are one grade above bitumen (tar) which does not flow at ambient conditions. While the high density and viscosity of these crudes make them difficult to transport, in addition, their processing requires additional steps to conventional refining, including: heating the oil in excess of 500° C., multiple steps of fractionalization, thermal cracking and hydrotreatment. These processing steps result in a low energy return on energy invested (EROEI) of about 5 (in comparison to ˜10 for conventional oils currently and as high as 20 historically). Because of the enormous amounts of heavy oil reserves in the world, but the lack of cost-effective technologies many techniques are being investigated to more effectively upgrade the heavy oils as noted above. A problem of heavy oil is that it takes large amounts of thermal energy and expensive catalysts to upgrade, in addition to the transportation costs. Therefore, new technologies are being sought for several reasons: 1) implementation in the refinery at lower temperatures 2) less sensitivity to oil contaminants 3) implementation prior to transportation, either, down-hole or at the well head rather than in the refinery, as this will lower transportation costs.
Thermal cracking is the process in which long hydrocarbon chains (heavy hydrocarbons) are broken into shorter simpler molecules (light hydrocarbons). It occurs through the breaking of carbon-carbon bonds in the original molecule. Typically this is done with temperature and catalysts. Done in the presence of hydrogen this is called hydrotreating and results in saturated hydrocarbons such as alkanes and naphthenes. Done with steam in short residence time reactors (hydrocracking) this process is used to treat heavier hydrocarbons to produce ethylene, at high temperatures (˜900° C.), or liquid hydrocarbons for use in gasoline or fuel oil, at lower temperatures. In cracking various chains of reactions takes place initiated by the formation of a radical as shown in Table 1 for a simple hydrocarbon (though similar processes occur for longer hydrocarbons). A single initiation reaction may feed several additional, decomposition and abstraction reactions before terminating.
TABLE 1Main Reactions in Hydrocarbon CrackingInitiationCH3CH3 → 2 CH3•Hydrogen AbstractionCH3• + CH3CH3 → CH4 + CH3CH2•RadicalCH3CH2• → CH2═CH2 + H•DecompositionRadical AdditionCH3CH2• + CH2═CH2 → CH3CH2CH2CH2•Termination -CH3• + CH3CH2• → CH3CH2CH3RecombinationTermination -CH3CH2• + CH3CH2• → CH2═CH2 + CH3CH3Disproportionation
‘Non-Thermal’ or ‘cold plasma’ cracking is generally similar to thermal cracking except that the initiation reaction occurs due to impact with a plasma produced species such as an electron, ion, photon, or electrically or vibrationally excited state which is not in equilibrium with the bulk of the matter being treated. The plasma treatment of gaseous hydrocarbons or vaporized liquid fuels is well known. The non-equlibirum nature of the plasma allow for significantly more efficient and rapid chemical reactions than an equilibrium system at similar temperature. Also the chemical reaction pathways in a non-thermal plasma can be more numerous than in a equilibrium system. Significantly less research has been done on the direct upgrading of liquid fuels using non-thermal plasma methods of hydrocarbon cracking. One of the few examples is the work by Kong et al., “Plasma Processing of Hydrocarbons”, Electric Power, 2009, in which a dielectric barrier discharge was generated in methane over a film of oil for the purpose of upgrading the oil. As shown in their results, the formation of shorter hydrocarbon chains is clearly observable. These results are promising. The economics/efficiencies of the process however are not assessed.
Plasma discharges submerged in liquids are a subset of plasma liquid interactions which more generally include other systems such as discharges near liquid surfaces, discharges in gases with aerosolized droplets and discharges onto a liquid surface. Generally such submerged plasma discharge systems are well known, consisting of electrodes submerged in a liquid, and may either generate a plasma from gas bubble injected into the liquid or through the dielectric breakdown of the liquid potentially with bubble formation but without bubble addition. Generally they consist of discharge between two stationary electrodes connected to an_external circuit. The discharges in such systems are generally very non-uniform and most such systems have very high energy released (on the order of Joules) during the discharge process. Only recent systems employing nanoscale electrode and nanosecond pulsing can achieve mJ energy releases [Nature—News and View: “Analytical Chemistry: Plasma Bubbles Detect Elements”, Nature 455, 1185-1186 (30 October 2008)]. Systems using mobile charge carriers rather than connected electrodes to initiate the discharges have not been studied. The prior art is also devoid of strategies for controlling discharge energies to levels an order of magnitude below the mJ level.
It is therefore an object of the present invention to provide an alternative advantageous process for the plasma processing of dielectric fluids, fuels, and especially heavy crude oils, to recover more desirable products.